US20050227155A1 - Electrophoretic particles, electrophoretic dispersion liquid, and electrophoretic display device - Google Patents
Electrophoretic particles, electrophoretic dispersion liquid, and electrophoretic display device Download PDFInfo
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- US20050227155A1 US20050227155A1 US11/100,589 US10058905A US2005227155A1 US 20050227155 A1 US20050227155 A1 US 20050227155A1 US 10058905 A US10058905 A US 10058905A US 2005227155 A1 US2005227155 A1 US 2005227155A1
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- electrophoretic
- display device
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on translational movement of particles in a fluid under the influence of an applied field
- G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
- G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G17/00—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process
- G03G17/04—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process using photoelectrophoresis
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
- Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
- Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
- Y10T428/2995—Silane, siloxane or silicone coating
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
- Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
- Y10T428/2996—Glass particles or spheres
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
- Y10T428/2998—Coated including synthetic resin or polymer
Definitions
- the present invention relates to electrophotographic particles, an electrophoretic dispersion liquid, and an electrophoretic display device using the electrophoretic particles and the electrophoretic dispersion liquid.
- liquid crystal display devices have been known and developed actively as a display device capable of meeting the needs by electrically controlling alignment of liquid crystal molecules to change optical characteristic of the liquid crystal and has been brought into the commercial stage.
- liquid crystal display devices are accompanied with such problems that they have poor viewability of characters on a picture area due to a viewing angle or reflection light and that an eyestrain problem caused by flickering, low luminance, etc., of a light source is not sufficiently solved.
- a multiplicity of electrophoretic particles which are positively charged and colored are dispersed in a space between a pair of substrates, each provided with an electrode, together with an electrophoretic dispersion liquid which is filled in the space and colored a color different from the color of the electrophoretic particles.
- a partition wall is formed so that it divides the space into a multiplicity of pixels-along a planar direction of the substrates.
- an electrophoretic display device when a positive-polarity voltage is applied to an observer's side electrode and a negative-polarity voltage is applied to an electrode on an opposite side, the positively charged electrophoretic particles are collected so as to cover the opposite side electrode, so that a color identical to the color of the electrophoretic dispersion liquid (dispersion medium) is displayed when the electrophoretic display device is observed from the observers side.
- any image or character is displayed by a multiplicity of pixels.
- an electrophoretic dispersion liquid is prepared by adding, e.g., an electrifying agent or a dispersing agent into an insulating dispersion medium to impart a chargeability (electrification characteristic) and a dispersibility to electrophoretic particles.
- the chargeability of the electrophoretic particles has been considered that it results from creation of zeta potential at particle surface by adsorption of dissociated electrifying agent onto the particle surface.
- the dispersibility has been considered that it results from steric-exclusion effect by adsorption of the added dispersing agent onto the particle surface.
- Japanese Laid-Open Patent Application No. (Tokuhyo Hei) 09-500458 has disclosed such a method that a chargeability and a dispersibility are imparted to pigment particles in an electrophoretic dispersion medium colored with a dye by using yellow pigment particles having an acidic site in combination with a charge control agent having a polymer chain containing a basic group.
- Japanese Laid-Open Patent Application No. (Tokkai) 2002-062545 has disclosed such a method that a chargeability and a dispersibility are imparted to particles in an electrophoretic dispersion liquid comprising a hydrocarbon solvent, particles having an acidic group (or a basic group), a basic (or acidic) polymer, and a compound having a nonionic polar group.
- the dispersibility is imparted to the electrophotographic particles by utilizing a salt (principally formed through proton transfer) formed by acid-base interaction between the electrophotographic particles and the additives and that the chargeability is imparted to the electrophotographic particles by dissociating a part of the salt from the formed salt.
- Such conventional electrophotographic particles utilizing the dissociation between acid and base or utilizing the electrifying agent have a small degree of dissociation in the insulating solvent, so that a resultant zeta potential is also small.
- the conventional electrophotographic particles have accompanied with a problem such that they have failed to respond to a voltage, applied under a low-voltage drive condition, at high speed.
- An object of the present invention is to provide electrophotographic particles capable of responding to a voltage, at high speed, applied thereto under a low-voltage drive condition.
- Another object of the present invention is to provide an electrophoretic dispersion liquid containing the electrophotographic particles and an electrophoretic display device using the electrophoretic dispersion liquid.
- the present invention has been accomplished by finding electrophotographic particles which are excellent in dissociation characteristic and zeta potential characteristic compared with the conventional electrophotographic particles utilizing the acid-base dissociation or the electrifying agent.
- electrophoretic particles each of which has a salt at a surface thereof, said salt comprising an acid-derived anionic group and any one of cationic compounds represented by the following formulas (1) to (4):
- an electrophoretic dispersion liquid comprising: the electrophotographic particles described above, and an insulating solvent in which the electrophotographic particles are dispersed.
- an electrophoretic display device comprising: a pair of substrates, and the electrophoretic dispersion liquid described above disposed between the pair of substrates.
- Each of the electrophotographic particles according to the present invention has an acidic group at least at a surface thereof and has such a structure that a salt is formed between the acidic group and any one of the above described compounds represented by the formulas (1) to (4).
- the resultant salt has a higher dissociation characteristic than the conventionally used acid-base salts, the electrifying agent, etc.
- a charging performance is improved to considerably improve a response speed of the electrophotographic particles, so that it is possible to provide the electrophotographic particles capable of responding to the applied voltage at high speed under a low-voltage drive condition and also provides the electrophoretic dispersion liquid containing the electrophotographic particles and the electrophoretic display device using the electrophoretic dispersion liquid.
- FIGS. 1 ( a ) and 1 ( b ) are schematic sectional views showing an embodiment of an electrophoretic display device using electrophoretic particles of the present invention.
- FIGS. 2 ( a ) and 2 ( b ) are schematic views showing a display example of the electrophoretic display device.
- FIGS. 3 ( a ) and 3 ( b ) are schematic sectional views showing another embodiment of an electrophoretic display device using electrophoretic particles of the present invention.
- FIGS. 4 ( a ) and 4 ( b ) are schematic views showing a display example of the electrophoretic display device of Second Embodiment.
- FIGS. 1 ( a ) and 1 ( b ) are schematic sectional views each showing an embodiment of an electrophoretic display device using electrophoretic particles according to the present invention.
- the electrophoretic display device includes a first substrate 1 a provided with a first electrode 1 c , a second substrate 1 b provided with a second electrode 1 d , and a partition wall 1 g disposed so that the first and second substrates 1 and 2 are oppositely disposed with a predetermined spacing.
- an electrophoretic dispersion liquid which at least comprises a plurality of electrophoretic particles 1 e and an electrophoretic dispersion medium 1 f .
- an insulating layer 1 h is formed on each of the first and second electrodes.
- a display surface of the electrophoretic display device is located on the second substrate 1 b side.
- FIG. 1 ( b ) shows an electrophoretic display device using microcapsules.
- a plurality of microcapsules 1 i each containing the electrophoretic dispersion liquid are disposed and covered with a second substrate 1 b .
- an insulating layer 1 h may be omitted.
- the first electrode 1 c is a pixel electrode and comprises a plurality of electrode portions which are independently capable of applying a desired electric field to the electrophoretic dispersion liquid in an associated cell (or microcapsule) of the respective cells.
- the second electrode 1 d is a common electrode through which the same electric potential is applied to the entire display area.
- the first electrode 1 c (pixel electrode) is provided with an unshown switching element (for each electrode portion) and is supplied with a selection signal from an unshown matrix drive circuit row by row and also supplied with a control signal and an output from an unshown drive transistor column by column.
- an unshown switching element for each electrode portion
- a control signal and an output from an unshown drive transistor column by column As a result, it is possible to apply a desired electric field to the electrophoretic dispersion liquid (electrophoretic particles 1 e ) in each of the cells groups.
- the electrophoretic particles 1 e in each individual cell (or microcapsule) are controlled by an electric field applied through the first electrode 1 c , whereby at each pixel, the color (e.g., white) of the electrophoretic particles 1 e and the color (e.g., blue) of the electrophoretic dispersion medium 1 f are selectively displayed.
- the color e.g., white
- the color e.g., blue
- the first substrate 1 a is formed of any insulating member, for supporting the electrophoretic display device, such as glass, plastic, or the like.
- the first electrode 1 c may be formed of a metal (vapor) deposition film of ITO (indium tin oxide), tin oxide, indium oxide, gold, chromium, etc., in a predetermined pattern through a photolithographic process.
- the second substrate 1 b may comprise an insulating member, such as a transparent glass substrate or a transparent plastic substrate.
- the second electrode 5 may be a transparent electrode formed of ITO film or an organic electroconductive film.
- the insulating layer 1 h can be formed of a colorless transparent insulating resin, such as acrylic resin, epoxy resin, fluorine-based resin, silicone resin, polyimide resin, polystyrene resin, or polyalkene resin.
- a colorless transparent insulating resin such as acrylic resin, epoxy resin, fluorine-based resin, silicone resin, polyimide resin, polystyrene resin, or polyalkene resin.
- the partition wall 1 g can be formed of a polymeric material through, e.g., a method wherein the partition wall is formed with a photosensitive resin through the photolithographic process, a method wherein the partition wall which has been prepared in advance is bonded to the substrate, a method wherein the partition wall is formed through molding, or the like.
- the method of filling the electrophoretic dispersion liquid is not particularly limited but can be an ink jet method using nozzles.
- microcapsule 1 i containing therein the electrophoretic dispersion liquid described above can be prepared through a known method, such as interfacial polymerization, in situ polymerization, coacervation, or the like.
- a high light-transmissive material may preferably be used.
- examples thereof may include: urea-formaldehyde resin, melamine-formaldehyde resin, polyester, polyurethane, polyamide, polyethylene, polystyrene, polyvinyl alcohol, gelatin, their copolymers, and so on.
- the method of forming the microcapsules on the first substrate 1 a is not particularly restricted but may be an ink jet method using nozzles.
- a liquid which is high insulative and colorless and transparent, including: aromatic hydrocarbons, such as toluene, xylene, ethylbenzene and dodecylbenzene; aliphatic hydrocarbons, such as hexane, cyclohexane, kerosine, normal paraffin and isoparaffin; halogenated hydrocarbons, such as chloroform, dichloromethane, pentachloroethane, 1,2-dibromoethane, 1,1,2,2-tetraburomoethane, trichloroethylene, tetrachloroethylene, trifluoroethylene and tetrafluoroethylene, various natural or synthetic oils, etc. These may be used singly or in mixture of two or more species.
- aromatic hydrocarbons such as toluene, xylene, ethylbenzene and dodecylbenzene
- aliphatic hydrocarbons such as hexane, cycl
- the electrophoretic dispersion medium 1 f may be colored with oil soluble dye having a color of R (red), G (green), B (blue), C (cyan), M (magenta), Y (yellow), etc.
- the dye may preferably include azo dyes, anthraquinone dyes, quinoline dyes, nitro dyes, nitroso dyes, penoline dyes, phthalocyanine dyes, metal complex salt dyes, naphthol dyes, benzoquinone dyes, cyanine dyes, indigo dyes, quinoimine dyes, etc. These may be used in combination.
- oil soluble dye examples include Vari Fast Yellow (1101, 1105, 3108, 4120), Oil Yellow (105, 107, 129, 3G, GGS), Vari Fast Red (1306, 1355, 2303, 3304, 3306, 3320), Oil Pink 312, Oil Scarlet 308, Oil Violet 730, Vari Fast Blue (1501, 1603, 1605, 1607, 2606, 2610, 3405). Oil Blue (2N, BOS, 613), Macrolex Blue RR, Sumiplast Gren G, Oil Green (502, BG), etc. A concentration of these dyes may preferably be 0.1-3.5 wt. %, per the electrophoretic dispersion medium 1 f.
- the electrophoretic particles 1 e used in the present invention it is possible to use particles each having an acidic group at least at a surface thereof, such as particles comprising a polymer having an acidic group and a pigment dispersed in the polymer, and particles comprising a polymer which has an acidic group and is colored with a dye, etc.
- the particles comprising the polymer having the acidic group and the pigment dispersed in the polymer may be obtained by polymerizing an acidic monomer containing the pigment or a basic monomer containing the pigment, e.g., through suspension polymerization, emulsion polymerization, deposition polymerization, dispersion polymerization, etc.
- the polymer having the acidic group used for such particles it is possible to use homopolymers of acidic monomers, such as (meth)acrylic acid, 2-butenoic acid (crotonic acid), 3-butenoic acid, (vinyl acetate), 3-methyl-3-butenoic acid, 3-pentenoic acid, 4-pentenoic acid, 4-methyl-4-pentenoic acid, 4-hexenoic acid, 5-hexenoic acid, 5-methyl-5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 6-methyl-6-heptenoic acid, 6-octenoic acid, 7-octenoic acid, 7-methyl-7-octenoic acid, 7-nonenoic acid, 8-nonenoic acid, 8-methyl-8-nonenoic acid, 8-decenoic acid, 9-decenoic acid, 3-phenyl-2-propenoic (cinnamic acid), carboxymethyl(meth)acrylate, carb
- copolymers of the above described acidic monomers with a monomer, such as methyl(meth-)acrylate, ethyl (meth)-acrylate, styrene, p-methyl styrene, p-ethyl styrene, acrylonitrile, etc.
- the pigment it is possible to use an organic pigment, an inorganic pigment, etc.
- organic pigment may include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments isoindolin pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, anthraquinone pigments, nitro pigments, and nitroso pigments.
- red pigments such as Quinacridone Red, Lake Red, Brilliant Carmine, Perylene Red, Permanent Red, Toluidine Red and Madder Lake
- green pigments such as Diamond Green Lake, Phthalocyanine Green, and Pigment Green
- blue pigments such as Victoria Blue Lake, Phthalocyanine Blue, and Fast Sky Blue
- yellow pigments such as Hansa Yellow, Fast Yellow, Disazo Yellow, Isoindolinone Yellow, an Quinophthalone Yellow
- black pigments such as Aniline Block and Diamond Black.
- the inorganic pigment may include: white pigments, such as titanium oxide, aluminum oxide, zinc oxide, lead oxide, and zinc sulfide; black pigments, such as carbon black, manganese ferrite block, cobalt ferrite black, and titanium black; red pigments, such as cadmium red, red iron oxide, and molybdenum red; green pigments, such as chromium oxide, viridian, titanium cobalt green, cobalt green, and victoria green; blue pigments, such as ultramarine blue, prussian blue, and cobalt blue; and yellow pigments, such as cadmium yellow, titanium yellow, yellow iron oxide, chrome yellow, and antimony yellow.
- white pigments such as titanium oxide, aluminum oxide, zinc oxide, lead oxide, and zinc sulfide
- black pigments such as carbon black, manganese ferrite block, cobalt ferrite black, and titanium black
- red pigments such as cadmium red, red iron oxide, and molybdenum red
- the particles comprising the polymer, having the acidic group, colored with a dye it is possible to use, e.g., particles comprising polymer particles, having the acidic group, colored with a dye or particles obtained through polymerization of an acidic monomer containing a dye.
- the dye is not particularly limited so long as it is not soluble in the electrophoretic dispersion medium 1 f .
- the monomer materials described above therefor it is possible to use the monomer materials described above therefor.
- the electrophotographic particles 1 e are obtained by causing such particles having the acidic group to react with a halide or hydroxide of the compounds represented by the structural formulas (1) to (3) or with a trialkylamine represented by the structural formula (5).
- the acidic group means sulfonic group or carboxyl group.
- Electrophotographic particles each having an imidazolium salt are prepared from electrophotographic particles each having sulfonic group and the halide compound of the imidazolium ion of the structural formula (1) according to the following chemical reaction formula (1): Chemical Reaction Formula (1)
- reaction solvent is not particularly limited but may preferably be alcohol, such as methanol or ethanol.
- X ⁇ represents halogen ion.
- each of R1 and R2 is a linear or branched alkyl group having 1-18 carbon atoms and may be the same or different from each other.
- Electrophotographic particles each having a pyridinium salt are prepared from electrophotographic particles each having sulfonic group and the halide compound of the pyridinium ion of the structural formula (2) according to the following chemical reaction formula (2): Chemical Reaction Formula (2)
- reaction solvent is not particularly limited but may preferably be the alcohol described above.
- X ⁇ represents halogen ion.
- R3 is a linear or branched alkyl group having 4-18 carbon atoms and R4 is a linear or branched alkyl group having 1-18 carbon atoms.
- Electrophotographic particles each having a quaternary ammonium salt are prepared from electrophotographic particles each having sulfonic group and the halide or hydroxide compound of the quaternary ammonium ion of the structural formula (3) according to the following chemical reaction formula (3): Chemical Reaction Formula (3)
- reaction solvent is not particularly limited but may preferably be the alcohol described above.
- X ⁇ represents halogen ion or hydroxide ion.
- each of R5, R6, R7 and R8 is a linear or branched alkyl group having 6-18 carbon atoms and may be the same or different from each other.
- Electrophotographic particles each having a tertiary ammonium salt are prepared from electrophotographic particles each having sulfonic group and the trialkylamine of the structural formula (5) according to the following chemical reaction formula (4): Chemical Reaction Formula (4)
- reaction solvent is not particularly limited but may preferably be alcohol, such as methanol or ethanol.
- each of R9, R10 and R11 is a linear or branched alkyl group having 4-18 carbon atoms and may be the same or different from each other.
- the above described electrophotographic particles 1 e of the present invention have excellent dissociation characteristic in the insulating electrophoretic dispersion medium 1 f . More specifically, the electrophotographic particles 1 e have a degree of dissociation which is several times to about 90 times that of zirconium octoate which has been ordinarily used conventionally.
- the electrophotographic particles 1 e may preferably have an average particle size of 50 nm to 10 ⁇ m, more preferably 300 nm to 2 ⁇ m. When the average particle size exceeds 10 ⁇ m, display at high resolution cannot be performed. When the average particle size is less than 50 nm, there arises an undesirable problem in terms of dispersion stability due to agglomeration of the particles.
- the electrophotographic particles 1 e may preferably have a concentration of 1-40 wt. %, more preferably 3-20 wt. %, per the weight of the electrophoretic dispersion medium 1 f .
- a display contrast of the electrophotographic particles 1 e is undesirably lowered.
- a display contrast of the colored electrophoretic dispersion medium 1 f is undesirably lowered.
- the dispersion stabilizer it is possible to use a homopolymer, a copolymer, a block polymer, etc.
- examples thereof may include: polyvinyl pyrrolidone, polyvinyl methyl ether, (styrene-vinylpyridine) copolymer, (styrene-butadiene)-copolymer, etc.
- the steric hindrance group it is possible to use a monomer, examples of which may include: 2-ethylhexyl(meth-)acrylate, octyl (meth-)acrystal, decyl(meth-)acrylate, dodecyl (meth-)acrylate, tetradecyl(meth-)acrylate, hexadecyl (meth-)acrylate, octadecyl(meth-)acrylate, butadiene, isoprene, isobutene, pentene, hexene, etc.
- the steric hindrance group can be introduced onto the electrophotographic particles 1 e by copolymerization thereof with the acidic monomer described above.
- FIGS. 2 ( a ) and 2 ( b ) A display example of the electrophoretic display device using the electrophotographic particles of the present invention i shown in FIGS. 2 ( a ) and 2 ( b ), wherein an EDL comprising white electrophotographic particles 1 e and an electrophoretic dispersion medium 1 f colored with a blue dye is filled in a cell.
- the electrophotographic particles 1 e are negatively charged by dissociation of the salt.
- the second electrode 1 d is 0 V and the first electrode 1 c is supplied with a voltage of a negative polarity, the electrophotographic particles 1 e are collected to the second electrode 1 d .
- the cell looks white due to distribution of the white electrophotographic particles 1 e .
- the electrophotographic particles 1 e are collected to the first electrode 1 c .
- the cell looks blue.
- FIGS. 4 ( a ) and 4 ( b ) are schematic sectional views each showing another embodiment of an electrophoretic display device using the electrophotographic particles of the present invention.
- the electrophoretic display device includes a first substrate 3 a on which a first electrode 3 c and a second electrode 3 d are disposed. Between the electrodes 3 c and 3 d and on the second electrode 3 d , an insulating layer 3 h and an insulating layer 3 i are formed, respectively.
- the insulating layer 3 h formed between the electrodes 3 c and 3 d may be colored or may be colorless and transparent, but the insulating layer 3 i is colorless and transparent.
- the electrophoretic display device further includes a second substrate 3 b disposed opposite to the first substrate 3 a with a spacing through a partition wall 3 g .
- a cell (space) defined by the pair of first and second substrates 3 a and 3 b and the partition wall 3 g an electrophoretic dispersion liquid comprising at least electrophoretic particles 3 e and an electrophoretic dispersion medium 3 f is sealed.
- a display surface of the electrophoretic display device is located on the second substrate 3 b side.
- FIG. 3 ( b ) shows an electrophoretic display device using microcapsules.
- a plurality of microcapsules 3 i each containing the electrophoretic dispersion liquid are disposed and covered with a second substrate 3 b .
- an insulating layer 3 i may be omitted.
- the second electrode 3 d comprises a plurality of electrode portions as pixel electrodes capable of independently applying a described electric field to the electrophoretic dispersion liquid in each cell (or each microcapsule), and the first electrode 3 c is a common electrode through which the same potential is applied to the entire display area.
- the second electrode 3 c (pixel electrode) is provided with an unshown switching element (for each electrode portion) and is supplied with a selection signal from an unshown matrix drive circuit row by row and also supplied with a control signal and an output from an unshown drive transistor column by column.
- an unshown switching element for each electrode portion
- the electrophoretic particles 3 e in each individual cell (or microcapsule) are controlled by an electric field applied through the second electrode 3 c , whereby at each pixel, the color (e.g., black) of the electrophoretic particles 3 e and the color (e.g., white) of the insulating layer 3 h are selectively displayed.
- the color e.g., black
- the color e.g., white
- the first substrate 3 a is formed of any insulating member, for supplying the electrophoretic display device, such a glass, plastic, or the like.
- the second substrate 3 b may be a transparent substrate or a transparent plastic substrate.
- the first electrode 3 c is a metal electrode of, e.g., Al exhibiting light reflection performance.
- the insulating layer 3 h formed on the first electrode 3 c is formed of a mixture of a transparent colorless insulating resin with light scattering fine particles of, e.g., aluminum oxide or titanium oxide.
- a transparent colorless insulating resin As a material for the transparent colorless insulating resin, it is possible use the above described insulating resins. Alternatively, it is also possible to use a light scattering method utilizing unevenness at the surface of the metal electrode without using the fine particles.
- the second electrode 3 d is formed of an electroconductive material, which looks dark black from the viewer side of the electrophoretic display device, such as titanium carbide, black-treated Cr, and Al or Ti provided with a black surface layer. Pattern formation of the second electrode 5 may be performed through a photolithographic process.
- the insulating layer 3 i is formed of, e.g., the transparent colorless insulating resin described above.
- a display contrast is largely depend on an areal ratio between the second electrode 3 d (each electrode portion) and an associated pixel, so that an exposed area of the second electrode 3 d is required to be smaller than that of the pixel in order to enhance a contrast. For this reason, it is preferable that the areal ratio therebetween may ordinarily be 1:2 to 1:5.
- the partition wall 3 g may be formed in the same manner as described above.
- the method of filling the above described electrophoretic dispersion liquid in the cell is not limited particularly but may be the above described ink jet method using nozzles.
- the microcapsule 3 j containing the electrophoretic dispersion liquid can be prepared by the known method as described above, such as interfacial polymerization, in situ polymerization, coacervation, and so on.
- the material for forming the microcapsule 3 j may be the same polymer as described above.
- the method of forming the microcapsules 3 j on the first substrate 3 a is not particularly restricted but may be the above described ink jet method using nozzles.
- a concentration of the electrophotographic particles 3 e may preferably 0.5-10 wt. %, more preferably 1-5 wt. %, per the weight of the electrophoretic dispersion medium 3 f .
- the concentration of the electrophotographic particles 3 e is less than 0.5 wt. %, the first electrode 3 c cannot be covered, so that a display contrast is undesirably lowered.
- the concentration of the electrophotographic particles 3 e exceeds 10 wt. %, the electrophotographic particles extend off the colored second electrode 3 d , thus undesirably lowering the display contrast.
- FIGS. 4 ( a ) and 4 ( b ) illustrate a display example wherein, e.g., an electrophoretic dispersion liquid comprising black electrophoretic particles 3 e and a colorless and transparent electrophoretic dispersion medium 3 f is filled in a cell.
- the electrophoretic particles 3 e is negatively charged by the dissociation of the salt.
- a uniform mixture liquid was prepared by mixing 15 g of titanium oxide particles (average particle size: 0.2 ⁇ m) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 7 g of methacrylic acid and 130 g of methyl methacrylate.
- AIBN azobisisobutyronitrile
- a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein.
- the resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension.
- the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere.
- the resultant polymer particles were washed, followed by drying and classification to obtain white particles each comprising titanium oxide particle coated with (methacrylic acid-methyl methacrylate) copolymer.
- An average particle size of the particles was about 2 microns.
- an electrophoretic dispersion medium 1 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) colored blue with 0.1 wt. % of a colorant (“Oil Blue N”, mfd. by Aldrich Co.) dissolved therein, were mixed to prepare an electrophoretic dispersion liquid.
- the electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in FIG. 1 ( a ), which was connected with a voltage application circuit.
- the electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- a plurality of microcapsules 1 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 1 were prepared by in-situ polymerization method. Each microcapsule was formed of urea-formaldehyde resin as a film-forming material.
- An electrophoretic display device shown in FIG. 1 ( b ) was prepared by disposing the plurality of microcapsules 1 i on a first substrate 1 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit.
- the electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- Particles of titanium oxide, coated with (methacrylic acid-methyl methacrylate) copolymer, prepared in the same manner as in Example 1 was subjected to two-stage polymerization with 2-ethylhexyl methacrylate to form a core-shell structure wherein a steric hindrance group was introduced into a surface of particle.
- an electrophoretic dispersion medium 1 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) colored blue with 0.1 wt. % of a colorant (“Oil Blue N”, mfd. by Aldrich Co.) dissolved therein, were mixed to prepare an electrophoretic dispersion liquid.
- the electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in FIG. 1 ( a ), which was connected with a voltage application circuit.
- the electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- a plurality of microcapsules 1 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 3 were prepared by in-situ polymerization method. Each microcapsule was formed of urea-formaldehyde resin as a film-forming material.
- An electrophoretic display device shown in FIG. 1 ( b ) was prepared by disposing the plurality of microcapsules 1 i on a first substrate 1 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit.
- the electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- a uniform mixture liquid was prepared by mixing 10 g of carbon black particles (average particle size: 30 nm) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 7 g of sodium styrenesulfonate and 130 g of styrene.
- AIBN azobisisobutyronitrile
- a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein.
- the resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension.
- the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere.
- the resultant polymer particles were washed, followed by drying and classification to obtain black particles each comprising carbon black particle coated with (sodium styrene sulfonate-styrene) copolymer.
- An average particle size of the particles was about 2 microns.
- the particles were subjected to acid treatment to convert the sodium sulfonate into sulfonic acid group.
- the quaternary ammonium salt of the structural formula (7) may be caused to react with the particles without converting the sodium sulfonate into the sulfonic acid group to obtain electrophotographic particles 3 each having the quaternary ammonium salt.
- an electrophoretic dispersion medium 3 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) were mixed to prepare an electrophoretic dispersion liquid.
- the electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in FIG. 3 ( a ), which was connected with a voltage application circuit.
- the electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- a plurality of microcapsules 3 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 5 were prepared by in-situ polymerization method. Each microcapsule was formed of polyamide resin as a film-forming material.
- An electrophoretic display device shown in FIG. 3 ( b ) was prepared by disposing the plurality of microcapsules 3 i on a first substrate 3 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit.
- the electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- Particles of carbon black, coated with (sodium styrenesulfonate-styrene) copolymer, prepared in the same manner as in Example 5 was subjected to two-stage polymerization with dodecyl methacrylate to form a core-shell structure wherein a steric hindrance group was introduced into a surface of particle.
- the particles were then subjected to acid treatment to convert the sodium sulfonate salt into sulfonic acid group.
- an electrophoretic dispersion liquid 1 wt. % of the black electrophoretic particles 3 e and 99 wt. % of an electrophoretic dispersion medium 3 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) mixed to prepare an electrophoretic dispersion liquid.
- the electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in FIG. 3 ( a ), which was connected with a voltage application circuit.
- the electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- a plurality of microcapsules 3 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 7 were prepared by in-situ polymerization method. Each microcapsule was formed of polyamide resin as a film-forming material.
- An electrophoretic display device shown in FIG. 3 ( b ) was prepared by disposing the plurality of microcapsules 3 i on a first substrate 3 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit.
- the electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed.
- a uniform mixture liquid was prepared by mixing 15 g of titanium oxide particles (average particle size: 0.2 ⁇ m) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 137 g of methyl methacrylate.
- AIBN azobisisobutyronitrile
- a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein.
- the resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension.
- the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere.
- the resultant polymer particles were washed, followed by drying and classification to obtain white particles each comprising titanium oxide particle coated with polymethyl methacrylate.
- An average particle size of the particles was about 2 microns.
- an electrophoretic dispersion medium comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) colored blue with 0.1 wt. % of a colorant (“Oil Blue N”, mfd. by Aldrich Co.) dissolved therein, were mixed to prepare an electrophoretic dispersion liquid.
- the electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in FIG. 1 ( a ), which was connected with a voltage application circuit.
- a uniform mixture liquid was prepared by mixing 10 g of carbon black particles (average particle size: 30 nm) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 135 g of styrene.
- AIBN azobisisobutyronitrile
- a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein.
- the resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension. Thereafter, the suspension was subjected to polymerization at 80° C.
- the resultant polymer particles were washed, followed by drying and classification to obtain black particles each comprising carbon black particle coated with polystyrene.
- An average particle size of the particles was about 2 microns.
- an electrophoretic dispersion medium comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) were mixed to prepare an electrophoretic dispersion liquid.
- the electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in FIG. 3 ( a ), which was connected with a voltage application circuit.
- the electrophotographic particles according to the present invention can be utilized in the field of electrophotography or the like using an electrophoretic display device or liquid toner.
- the salt of the electrophotographic particles of the present invention has an excellent dissociation characteristic in an insulating solvent compared with an acid-base salt or an electrifying used, so that a charging performance is improved. As a result, it becomes possible to provide a considerably higher response speed of the electrophotographic particles than conventional electrophotographic particles. By using the electrophotographic particles capable of effecting high-speed response, it is possible to realize an excellent electrophoretic display device or electrophotographic apparatus.
Abstract
Description
- The present invention relates to electrophotographic particles, an electrophoretic dispersion liquid, and an electrophoretic display device using the electrophoretic particles and the electrophoretic dispersion liquid.
- In recent years, with development of information equipment, the needs for low-power and thin display devices have grown, so that extensive study and development have been made on display devices fitted to these needs. Of these display devices, liquid crystal display devices have been known and developed actively as a display device capable of meeting the needs by electrically controlling alignment of liquid crystal molecules to change optical characteristic of the liquid crystal and has been brought into the commercial stage.
- However, such liquid crystal display devices are accompanied with such problems that they have poor viewability of characters on a picture area due to a viewing angle or reflection light and that an eyestrain problem caused by flickering, low luminance, etc., of a light source is not sufficiently solved.
- As one of the display devices, Harold D. Lees et al. (U.S. Pat. No. 3,612,758) have proposed an electrophoretic display device.
- In the electrophoretic display device, a multiplicity of electrophoretic particles which are positively charged and colored are dispersed in a space between a pair of substrates, each provided with an electrode, together with an electrophoretic dispersion liquid which is filled in the space and colored a color different from the color of the electrophoretic particles. In the space, a partition wall is formed so that it divides the space into a multiplicity of pixels-along a planar direction of the substrates. By forming such a partition wall, it is possible to define the space between the pair of substrates while preventing localization of the electrophoretic particles.
- In such an electrophoretic display device, when a positive-polarity voltage is applied to an observer's side electrode and a negative-polarity voltage is applied to an electrode on an opposite side, the positively charged electrophoretic particles are collected so as to cover the opposite side electrode, so that a color identical to the color of the electrophoretic dispersion liquid (dispersion medium) is displayed when the electrophoretic display device is observed from the observers side.
- On the other hand, when a negative-polarity voltage is applied to the observer's side electrode and a positive-polarity voltage is applied to the opposite side electrode, the positively charged electrophoretic particles are collected so as to cover the observer's side electrode, so that a color identical to the color of the electrophoretic particles is displayed when the electrophoretic display device is observed from the observer's side.
- By performing such a drive of the electrophoretic display device on a pixel-by-pixel basis, any image or character is displayed by a multiplicity of pixels.
- In a conventional electrophoretic display device, an electrophoretic dispersion liquid is prepared by adding, e.g., an electrifying agent or a dispersing agent into an insulating dispersion medium to impart a chargeability (electrification characteristic) and a dispersibility to electrophoretic particles. The chargeability of the electrophoretic particles has been considered that it results from creation of zeta potential at particle surface by adsorption of dissociated electrifying agent onto the particle surface. On the other hand, the dispersibility has been considered that it results from steric-exclusion effect by adsorption of the added dispersing agent onto the particle surface.
- Japanese Laid-Open Patent Application No. (Tokuhyo Hei) 09-500458 has disclosed such a method that a chargeability and a dispersibility are imparted to pigment particles in an electrophoretic dispersion medium colored with a dye by using yellow pigment particles having an acidic site in combination with a charge control agent having a polymer chain containing a basic group.
- Further, Japanese Laid-Open Patent Application No. (Tokkai) 2002-062545 has disclosed such a method that a chargeability and a dispersibility are imparted to particles in an electrophoretic dispersion liquid comprising a hydrocarbon solvent, particles having an acidic group (or a basic group), a basic (or acidic) polymer, and a compound having a nonionic polar group.
- As described above, there have been conventionally known that the dispersibility is imparted to the electrophotographic particles by utilizing a salt (principally formed through proton transfer) formed by acid-base interaction between the electrophotographic particles and the additives and that the chargeability is imparted to the electrophotographic particles by dissociating a part of the salt from the formed salt.
- Such conventional electrophotographic particles utilizing the dissociation between acid and base or utilizing the electrifying agent have a small degree of dissociation in the insulating solvent, so that a resultant zeta potential is also small. As a result, the conventional electrophotographic particles have accompanied with a problem such that they have failed to respond to a voltage, applied under a low-voltage drive condition, at high speed.
- An object of the present invention is to provide electrophotographic particles capable of responding to a voltage, at high speed, applied thereto under a low-voltage drive condition.
- Another object of the present invention is to provide an electrophoretic dispersion liquid containing the electrophotographic particles and an electrophoretic display device using the electrophoretic dispersion liquid.
- The present invention has been accomplished by finding electrophotographic particles which are excellent in dissociation characteristic and zeta potential characteristic compared with the conventional electrophotographic particles utilizing the acid-base dissociation or the electrifying agent.
- According to an aspect of the present invention, there is provided electrophoretic particles, each of which has a salt at a surface thereof, said salt comprising an acid-derived anionic group and any one of cationic compounds represented by the following formulas (1) to (4):
-
- Formula (1):
wherein R1 and R2 independently denote a linear or branched alkyl group having 1-18 carbon atoms; - Formula (2):
wherein R3 denotes a linear or branched alkyl group having 4-18 carbon atoms, and R4 denotes a linear or branched alkyl group having 1-18 carbon atoms; - Formula (3):
wherein R5, R6, R7 and R8 independently denote a linear or branched alkyl group having 6-18 carbon atoms; and - Formula (4):
wherein R9, R10 and R11 independently denote a linear or branched alkyl group having 4-18 carbon atoms.
- Formula (1):
- According to another aspect of the present invention, there is provided an electrophoretic dispersion liquid, comprising: the electrophotographic particles described above, and an insulating solvent in which the electrophotographic particles are dispersed.
- According to a further aspect of the present invention, there is provided an electrophoretic display device, comprising: a pair of substrates, and the electrophoretic dispersion liquid described above disposed between the pair of substrates.
- Each of the electrophotographic particles according to the present invention has an acidic group at least at a surface thereof and has such a structure that a salt is formed between the acidic group and any one of the above described compounds represented by the formulas (1) to (4). The resultant salt has a higher dissociation characteristic than the conventionally used acid-base salts, the electrifying agent, etc. As a result, a charging performance is improved to considerably improve a response speed of the electrophotographic particles, so that it is possible to provide the electrophotographic particles capable of responding to the applied voltage at high speed under a low-voltage drive condition and also provides the electrophoretic dispersion liquid containing the electrophotographic particles and the electrophoretic display device using the electrophoretic dispersion liquid.
- These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
- FIGS. 1(a) and 1(b) are schematic sectional views showing an embodiment of an electrophoretic display device using electrophoretic particles of the present invention.
- FIGS. 2(a) and 2(b) are schematic views showing a display example of the electrophoretic display device.
- FIGS. 3(a) and 3(b) are schematic sectional views showing another embodiment of an electrophoretic display device using electrophoretic particles of the present invention.
- FIGS. 4(a) and 4(b) are schematic views showing a display example of the electrophoretic display device of Second Embodiment.
- Hereinbelow, preferred embodiments of the present invention will be described in detail with reference to the drawings.
- FIGS. 1(a) and 1(b) are schematic sectional views each showing an embodiment of an electrophoretic display device using electrophoretic particles according to the present invention.
- Referring to
FIG. 1 (a), the electrophoretic display device includes afirst substrate 1 a provided with afirst electrode 1 c, asecond substrate 1 b provided with asecond electrode 1 d, and apartition wall 1 g disposed so that the first and second substrates 1 and 2 are oppositely disposed with a predetermined spacing. - In a cell (space) defined by the first and
second substrates partition wall 1 g, an electrophoretic dispersion liquid which at least comprises a plurality ofelectrophoretic particles 1 e and anelectrophoretic dispersion medium 1 f. On each of the first and second electrodes, aninsulating layer 1 h is formed. A display surface of the electrophoretic display device is located on thesecond substrate 1 b side. -
FIG. 1 (b) shows an electrophoretic display device using microcapsules. On afirst substrate 1 a, a plurality ofmicrocapsules 1 i each containing the electrophoretic dispersion liquid are disposed and covered with asecond substrate 1 b. In the case of using the microcapsules, aninsulating layer 1 h may be omitted. - In
FIG. 1 , thefirst electrode 1 c is a pixel electrode and comprises a plurality of electrode portions which are independently capable of applying a desired electric field to the electrophoretic dispersion liquid in an associated cell (or microcapsule) of the respective cells. Thesecond electrode 1 d is a common electrode through which the same electric potential is applied to the entire display area. - The
first electrode 1 c (pixel electrode) is provided with an unshown switching element (for each electrode portion) and is supplied with a selection signal from an unshown matrix drive circuit row by row and also supplied with a control signal and an output from an unshown drive transistor column by column. As a result, it is possible to apply a desired electric field to the electrophoretic dispersion liquid (electrophoretic particles 1 e) in each of the cells groups. - The
electrophoretic particles 1 e in each individual cell (or microcapsule) are controlled by an electric field applied through thefirst electrode 1 c, whereby at each pixel, the color (e.g., white) of theelectrophoretic particles 1 e and the color (e.g., blue) of theelectrophoretic dispersion medium 1 f are selectively displayed. By effecting such a drive on a pixel-by-pixel basis, it is possible to effect display of arbitrary images and characters by use of corresponding pixels. - The
first substrate 1 a is formed of any insulating member, for supporting the electrophoretic display device, such as glass, plastic, or the like. - The
first electrode 1 c may be formed of a metal (vapor) deposition film of ITO (indium tin oxide), tin oxide, indium oxide, gold, chromium, etc., in a predetermined pattern through a photolithographic process. Thesecond substrate 1 b may comprise an insulating member, such as a transparent glass substrate or a transparent plastic substrate. The second electrode 5 may be a transparent electrode formed of ITO film or an organic electroconductive film. - The insulating
layer 1 h can be formed of a colorless transparent insulating resin, such as acrylic resin, epoxy resin, fluorine-based resin, silicone resin, polyimide resin, polystyrene resin, or polyalkene resin. - The
partition wall 1 g can be formed of a polymeric material through, e.g., a method wherein the partition wall is formed with a photosensitive resin through the photolithographic process, a method wherein the partition wall which has been prepared in advance is bonded to the substrate, a method wherein the partition wall is formed through molding, or the like. - The method of filling the electrophoretic dispersion liquid is not particularly limited but can be an ink jet method using nozzles.
- The
microcapsule 1 i containing therein the electrophoretic dispersion liquid described above can be prepared through a known method, such as interfacial polymerization, in situ polymerization, coacervation, or the like. - As a material for the
microcapsule 1 i, a high light-transmissive material may preferably be used. Examples thereof may include: urea-formaldehyde resin, melamine-formaldehyde resin, polyester, polyurethane, polyamide, polyethylene, polystyrene, polyvinyl alcohol, gelatin, their copolymers, and so on. - The method of forming the microcapsules on the
first substrate 1 a is not particularly restricted but may be an ink jet method using nozzles. - As the
electrophoretic dispersion medium 1 f, it is possible to use a liquid, which is high insulative and colorless and transparent, including: aromatic hydrocarbons, such as toluene, xylene, ethylbenzene and dodecylbenzene; aliphatic hydrocarbons, such as hexane, cyclohexane, kerosine, normal paraffin and isoparaffin; halogenated hydrocarbons, such as chloroform, dichloromethane, pentachloroethane, 1,2-dibromoethane, 1,1,2,2-tetraburomoethane, trichloroethylene, tetrachloroethylene, trifluoroethylene and tetrafluoroethylene, various natural or synthetic oils, etc. These may be used singly or in mixture of two or more species. - The
electrophoretic dispersion medium 1 f may be colored with oil soluble dye having a color of R (red), G (green), B (blue), C (cyan), M (magenta), Y (yellow), etc. Examples of the dye may preferably include azo dyes, anthraquinone dyes, quinoline dyes, nitro dyes, nitroso dyes, penoline dyes, phthalocyanine dyes, metal complex salt dyes, naphthol dyes, benzoquinone dyes, cyanine dyes, indigo dyes, quinoimine dyes, etc. These may be used in combination. - Examples of the oil soluble dye may include Vari Fast Yellow (1101, 1105, 3108, 4120), Oil Yellow (105, 107, 129, 3G, GGS), Vari Fast Red (1306, 1355, 2303, 3304, 3306, 3320), Oil Pink 312, Oil Scarlet 308, Oil Violet 730, Vari Fast Blue (1501, 1603, 1605, 1607, 2606, 2610, 3405). Oil Blue (2N, BOS, 613), Macrolex Blue RR, Sumiplast Gren G, Oil Green (502, BG), etc. A concentration of these dyes may preferably be 0.1-3.5 wt. %, per the
electrophoretic dispersion medium 1 f. - As the
electrophoretic particles 1 e used in the present invention, it is possible to use particles each having an acidic group at least at a surface thereof, such as particles comprising a polymer having an acidic group and a pigment dispersed in the polymer, and particles comprising a polymer which has an acidic group and is colored with a dye, etc. - The particles comprising the polymer having the acidic group and the pigment dispersed in the polymer may be obtained by polymerizing an acidic monomer containing the pigment or a basic monomer containing the pigment, e.g., through suspension polymerization, emulsion polymerization, deposition polymerization, dispersion polymerization, etc.
- As the polymer having the acidic group used for such particles, it is possible to use homopolymers of acidic monomers, such as (meth)acrylic acid, 2-butenoic acid (crotonic acid), 3-butenoic acid, (vinyl acetate), 3-methyl-3-butenoic acid, 3-pentenoic acid, 4-pentenoic acid, 4-methyl-4-pentenoic acid, 4-hexenoic acid, 5-hexenoic acid, 5-methyl-5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 6-methyl-6-heptenoic acid, 6-octenoic acid, 7-octenoic acid, 7-methyl-7-octenoic acid, 7-nonenoic acid, 8-nonenoic acid, 8-methyl-8-nonenoic acid, 8-decenoic acid, 9-decenoic acid, 3-phenyl-2-propenoic (cinnamic acid), carboxymethyl(meth)acrylate, carboxyethyl (meth)acrylate, vinyl benzoate, vinylphenyl acetate, vinylphenyl propionate, maleic acid, fumaric acid, methylenesuccinic acid (itaconic acid), hydroxystyrene, styrenesulfonic acid, vinyltoluenesulfonic acid, vinylsulfonic acid, sulfomethyl(meth)acrylate, 2-sulfoethyl(meth)acrylate, 2-propene-1-sulfonate, 2-methyl-2-propene-1-sulfonate, and 3-butene-1-sulfonate. It is also possible to use copolymers of the above described acidic monomers with a monomer, such as methyl(meth-)acrylate, ethyl (meth)-acrylate, styrene, p-methyl styrene, p-ethyl styrene, acrylonitrile, etc.
- As the pigment, it is possible to use an organic pigment, an inorganic pigment, etc.
- Examples of organic pigment may include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments isoindolin pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, anthraquinone pigments, nitro pigments, and nitroso pigments. Specific examples thereof may include: red pigments, such as Quinacridone Red, Lake Red, Brilliant Carmine, Perylene Red, Permanent Red, Toluidine Red and Madder Lake; green pigments, such as Diamond Green Lake, Phthalocyanine Green, and Pigment Green; blue pigments, such as Victoria Blue Lake, Phthalocyanine Blue, and Fast Sky Blue; yellow pigments, such as Hansa Yellow, Fast Yellow, Disazo Yellow, Isoindolinone Yellow, an Quinophthalone Yellow; and black pigments, such as Aniline Block and Diamond Black.
- Examples of the inorganic pigment may include: white pigments, such as titanium oxide, aluminum oxide, zinc oxide, lead oxide, and zinc sulfide; black pigments, such as carbon black, manganese ferrite block, cobalt ferrite black, and titanium black; red pigments, such as cadmium red, red iron oxide, and molybdenum red; green pigments, such as chromium oxide, viridian, titanium cobalt green, cobalt green, and victoria green; blue pigments, such as ultramarine blue, prussian blue, and cobalt blue; and yellow pigments, such as cadmium yellow, titanium yellow, yellow iron oxide, chrome yellow, and antimony yellow.
- As the particles comprising the polymer, having the acidic group, colored with a dye, it is possible to use, e.g., particles comprising polymer particles, having the acidic group, colored with a dye or particles obtained through polymerization of an acidic monomer containing a dye. The dye is not particularly limited so long as it is not soluble in the
electrophoretic dispersion medium 1 f. In order to obtain the polymer having the acidic monomer, it is possible to use the monomer materials described above therefor. - The
electrophotographic particles 1 e are obtained by causing such particles having the acidic group to react with a halide or hydroxide of the compounds represented by the structural formulas (1) to (3) or with a trialkylamine represented by the structural formula (5). Here, the acidic group means sulfonic group or carboxyl group. - Electrophotographic particles each having an imidazolium salt are prepared from electrophotographic particles each having sulfonic group and the halide compound of the imidazolium ion of the structural formula (1) according to the following chemical reaction formula (1):
Chemical Reaction Formula (1) - A reaction solvent is not particularly limited but may preferably be alcohol, such as methanol or ethanol.
- In the chemical formula (1), X− represents halogen ion.
-
- Examples of a preferred imidazolium ion may include 1-hexyl-3-methylimidazolium ion (R1=methyl, R2=n-hexyl), 1-octyl-3-methylimidazolium ion (R1=methyl, R2=n-octyl), 1-decyl-3-methylimidazolium ion (R1=methyl, R2=n-decyl), 1-dodecyl-3-methylimidazolium ion (R1=methyl, R2=n-dodecyl), 1-tetradecyl-3-methylimidazolium ion (R1=methyl, R2=n-tetradecyl), 1-hexadecyl-3-methylimidazolium ion (R1=methyl, R2=n-hexadecyl), 1-octadecyl-3-methylimidazolium ion (R1=methyl, R2=n-octadecyl), ethylimidazolium ion (R1=ethyl, R2=n-hexyl), 1-octyl-3-methylimidazolium ion (R1=methyl, R2=n-octyl), 1-decyl-3-methylimidazolium ion (R1=ethyl, R2=n-decyl), 1-dodecyl-3-methylimidazolium ion (R1=ethyl, R2=n-dodecyl), 1-tetradecyl-3-methylimidazolium ion (R1=ethyl, R2=n-tetradecyl), 1-hexadecyl-3-methylimidazolium ion (R1=ethyl, R2=n-hexadecyl), 1-octadecyl-3-methylimidazolium ion (R1=ethyl, R2=n-octadecyl).
-
- A reaction solvent is not particularly limited but may preferably be the alcohol described above.
- In the chemical formula (2), X− represents halogen ion.
-
- Examples of a preferred pyridinium ion may include: N-butylpyridinium ion (R3=n-butyl, R4=hydrogen), N-hexylpyridinium ion (R3=n-hexyl, R4=hydrogen), N-octylpyridinium ion (R3=n-octyl, R4=hydrogen), N-decylpyridinium ion (R3=n-decyl, R4=hydrogen), N-dodecylpyridinium ion (R3=n-dodecyl, R4=hydrogen), N-tetradecylpyridinium ion (R3=n-tetradecyl, R4=hydrogen), N-hexadecylpyridinium ion (R3=n-hexadecyl, R4=hydrogen), N-octadecylpyridinium ion (R3=n-octadecyl, R4=hydrogen), N-butyl-3-butylpyridinium ion (R3=R4=n-butyl), N-hexyl-3-butylpyridinium ion (R3=n-hexyl, R4=n-butyl), N-octyl-3-butylpyridinium ion (R3=n-octyl, R4=n-butyl), N-decyl-3-butylpyridinium ion (R3=n-decyl, R4=n-butyl), N-dodecyl-3-butylpyridinium ion (R3=n-dodecyl, R4=n-butyl), N-tetradecyl-3-butylpyridinium ion (R3=n-tetradecyl, R4=n-butyl), N-hexadecyl-3-butylpyridinium ion (R3=n-hexadecyl, R4=n-butyl), and N-octadecyl-3-butylpyridinium ion (R3=n-octadecyl, R4=n-butyl).
- Electrophotographic particles each having a quaternary ammonium salt are prepared from electrophotographic particles each having sulfonic group and the halide or hydroxide compound of the quaternary ammonium ion of the structural formula (3) according to the following chemical reaction formula (3):
Chemical Reaction Formula (3) - A reaction solvent is not particularly limited but may preferably be the alcohol described above.
- In the chemical formula (3), X− represents halogen ion or hydroxide ion.
-
- Examples of a preferred quaternary ammonium ion may include: tetra(n-octyl)ammonium ion (R5=R6=R7=R8=n-octyl), tetra(n-decyl)ammonium ion (R5=R6=R7=R8=n-decyl), tetra(n-dodecyl)ammonium ion (R5=R6=R7=R8=n-dodecyl), tetra(n-tetradecyl) ammonium ion (R5=R6=R7=R8=n-tetradecyl), tetra (n-hexadecyl)ammonium ion (R5=R6=R7=R8=n-hexadecyl), trimethyldecylammonium ion (R5=n-decyl, R6=R7=R8=methyl), trimethyldodecylammonium ion (R5=n-dodecyl, R6=R7=R8=methyl), trimethyl-tetradecylammonium ion (R5=n-tetradecyl, R6=R7=R8=methyl), trimethylhexadecylammonium ion (R5=n-hexadecyl, R6=R7=R8=methyl), and trimethyloctadecylammonium ion (R5=n-octadecyl, R6=R7=R8=methyl).
-
- A reaction solvent is not particularly limited but may preferably be alcohol, such as methanol or ethanol.
-
- Examples of a preferred trialkylamine may include: tri(n-butyl)amine (R9=R10=R11=n-butyl), tri(t-butyl)amine (R9=R10=R11=t-butyl), tri(iso-butyl)amine (R9=R10=R11=iso-butyl), tri(2-methylbutyl)amine (R9=R10=R11=2-methylbutyl), tri(2-ethylbutyl)amine (R9=R10=R11=2-ethylbutyl), tri(n-pentyl)amine (R9=R10, R11=n-pentyl), tri(n-hexyl)amine (R9=R10=R11=n-hexyl), tri(2-ethylhexyl)amine (R9=R10=R11=2-ethylhexyl), tri(n-octyl)amine (R9=R10=R11=n-octyl), and tri(n-decyl)amine (R9=R10=R11=n-decyl).
- The above described
electrophotographic particles 1 e of the present invention have excellent dissociation characteristic in the insulatingelectrophoretic dispersion medium 1 f. More specifically, theelectrophotographic particles 1 e have a degree of dissociation which is several times to about 90 times that of zirconium octoate which has been ordinarily used conventionally. - The
electrophotographic particles 1 e may preferably have an average particle size of 50 nm to 10 μm, more preferably 300 nm to 2 μm. When the average particle size exceeds 10 μm, display at high resolution cannot be performed. When the average particle size is less than 50 nm, there arises an undesirable problem in terms of dispersion stability due to agglomeration of the particles. - The
electrophotographic particles 1 e may preferably have a concentration of 1-40 wt. %, more preferably 3-20 wt. %, per the weight of theelectrophoretic dispersion medium 1 f. When the electrophotographic particles have the concentration of less than 1 wt. %, a display contrast of theelectrophotographic particles 1 e is undesirably lowered. When the concentration of the electrophotographic particles exceeds 40 wt. %, a display contrast of the coloredelectrophoretic dispersion medium 1 f is undesirably lowered. - With respect to dispersibility of the
electrophotographic particles 1 e in theelectrophoretic dispersion medium 1 f, it is possible to impart the dispersibility to theelectrophotographic particles 1 e by adding therein a dispersion stabilizer or introducing a steric hindrance group into the electrophotographic particles. - As the dispersion stabilizer, it is possible to use a homopolymer, a copolymer, a block polymer, etc. Examples thereof may include: polyvinyl pyrrolidone, polyvinyl methyl ether, (styrene-vinylpyridine) copolymer, (styrene-butadiene)-copolymer, etc.
- As the steric hindrance group, it is possible to use a monomer, examples of which may include: 2-ethylhexyl(meth-)acrylate, octyl (meth-)acrystal, decyl(meth-)acrylate, dodecyl (meth-)acrylate, tetradecyl(meth-)acrylate, hexadecyl (meth-)acrylate, octadecyl(meth-)acrylate, butadiene, isoprene, isobutene, pentene, hexene, etc. The steric hindrance group can be introduced onto the
electrophotographic particles 1 e by copolymerization thereof with the acidic monomer described above. - A display example of the electrophoretic display device using the electrophotographic particles of the present invention i shown in FIGS. 2(a) and 2(b), wherein an EDL comprising white
electrophotographic particles 1 e and anelectrophoretic dispersion medium 1 f colored with a blue dye is filled in a cell. In these figures, theelectrophotographic particles 1 e are negatively charged by dissociation of the salt. When thesecond electrode 1 d is 0 V and thefirst electrode 1 c is supplied with a voltage of a negative polarity, theelectrophotographic particles 1 e are collected to thesecond electrode 1 d. As a result, when the cell is viewed from above, the cell looks white due to distribution of thewhite electrophotographic particles 1 e. On the other hand, when thesecond electrode 1 d is 0 V and thefirst electrode 1 c is supplied with a voltage of a positive polarity, theelectrophotographic particles 1 e are collected to thefirst electrode 1 c. As a result, when the cell is viewed from above, the cell looks blue. By carrying out such a drive on a pixel-by-pixel basis, it is possible to display arbitrary image and character at a multiplicity of pixels. - Hereinbelow, another embodiment of an electrophoretic display device using electrophoretic particles of the present invention will be described with reference to the drawings.
- FIGS. 4(a) and 4(b) are schematic sectional views each showing another embodiment of an electrophoretic display device using the electrophotographic particles of the present invention.
- As shown in
FIG. 4 (a), the electrophoretic display device includes afirst substrate 3 a on which afirst electrode 3 c and asecond electrode 3 d are disposed. Between theelectrodes second electrode 3 d, an insulatinglayer 3 h and an insulatinglayer 3 i are formed, respectively. The insulatinglayer 3 h formed between theelectrodes layer 3 i is colorless and transparent. - The electrophoretic display device further includes a
second substrate 3 b disposed opposite to thefirst substrate 3 a with a spacing through apartition wall 3 g. In a cell (space) defined by the pair of first andsecond substrates partition wall 3 g, an electrophoretic dispersion liquid comprising at leastelectrophoretic particles 3 e and anelectrophoretic dispersion medium 3 f is sealed. A display surface of the electrophoretic display device is located on thesecond substrate 3 b side. -
FIG. 3 (b) shows an electrophoretic display device using microcapsules. On afirst substrate 3 a, a plurality ofmicrocapsules 3 i each containing the electrophoretic dispersion liquid are disposed and covered with asecond substrate 3 b. In the case of using the microcapsules, an insulatinglayer 3 i may be omitted. - In FIGS. 3(a) and 3(b), the
second electrode 3 d comprises a plurality of electrode portions as pixel electrodes capable of independently applying a described electric field to the electrophoretic dispersion liquid in each cell (or each microcapsule), and thefirst electrode 3 c is a common electrode through which the same potential is applied to the entire display area. - The
second electrode 3 c (pixel electrode) is provided with an unshown switching element (for each electrode portion) and is supplied with a selection signal from an unshown matrix drive circuit row by row and also supplied with a control signal and an output from an unshown drive transistor column by column. As a result, it is possible to apply a desired electric field to the electrophoretic dispersion liquid (electrophoretic particles 3 e) in each of the cells groups. - The
electrophoretic particles 3 e in each individual cell (or microcapsule) are controlled by an electric field applied through thesecond electrode 3 c, whereby at each pixel, the color (e.g., black) of theelectrophoretic particles 3 e and the color (e.g., white) of the insulatinglayer 3 h are selectively displayed. By effecting such a drive on a pixel-by-pixel basis, it is possible to effect display of arbitrary images and characters by use of corresponding pixels 3. - The
first substrate 3 a is formed of any insulating member, for supplying the electrophoretic display device, such a glass, plastic, or the like. - The
second substrate 3 b may be a transparent substrate or a transparent plastic substrate. - The
first electrode 3 c is a metal electrode of, e.g., Al exhibiting light reflection performance. - The insulating
layer 3 h formed on thefirst electrode 3 c is formed of a mixture of a transparent colorless insulating resin with light scattering fine particles of, e.g., aluminum oxide or titanium oxide. As a material for the transparent colorless insulating resin, it is possible use the above described insulating resins. Alternatively, it is also possible to use a light scattering method utilizing unevenness at the surface of the metal electrode without using the fine particles. - The
second electrode 3 d is formed of an electroconductive material, which looks dark black from the viewer side of the electrophoretic display device, such as titanium carbide, black-treated Cr, and Al or Ti provided with a black surface layer. Pattern formation of the second electrode 5 may be performed through a photolithographic process. - On the
second electrode 3 d, the insulatinglayer 3 i is formed of, e.g., the transparent colorless insulating resin described above. - In this embodiment, a display contrast is largely depend on an areal ratio between the
second electrode 3 d (each electrode portion) and an associated pixel, so that an exposed area of thesecond electrode 3 d is required to be smaller than that of the pixel in order to enhance a contrast. For this reason, it is preferable that the areal ratio therebetween may ordinarily be 1:2 to 1:5. - The
partition wall 3 g may be formed in the same manner as described above. The method of filling the above described electrophoretic dispersion liquid in the cell is not limited particularly but may be the above described ink jet method using nozzles. - The
microcapsule 3 j containing the electrophoretic dispersion liquid can be prepared by the known method as described above, such as interfacial polymerization, in situ polymerization, coacervation, and so on. The material for forming themicrocapsule 3 j may be the same polymer as described above. - The method of forming the
microcapsules 3 j on thefirst substrate 3 a is not particularly restricted but may be the above described ink jet method using nozzles. - As the
electrophoretic dispersion medium 3 f, it is possible to use the above described liquids, and as theelectrophoretic particles 3 e, it is possible to use the above described particles. In this embodiment, a concentration of theelectrophotographic particles 3 e may preferably 0.5-10 wt. %, more preferably 1-5 wt. %, per the weight of theelectrophoretic dispersion medium 3 f. When the concentration of theelectrophotographic particles 3 e is less than 0.5 wt. %, thefirst electrode 3 c cannot be covered, so that a display contrast is undesirably lowered. Further, when the concentration of theelectrophotographic particles 3 e exceeds 10 wt. %, the electrophotographic particles extend off the coloredsecond electrode 3 d, thus undesirably lowering the display contrast. - A display example of the electrophoretic display device using the electrophoretic particles liquid according to this embodiment is shown in FIGS. 4(a) and 4(b).
- FIGS. 4(a) and 4(b) illustrate a display example wherein, e.g., an electrophoretic dispersion liquid comprising black
electrophoretic particles 3 e and a colorless and transparentelectrophoretic dispersion medium 3 f is filled in a cell. Theelectrophoretic particles 3 e is negatively charged by the dissociation of the salt. - In the case where the color of the surface of the insulating
layer 3 a is white and the color of the surface of thesecond electrode 3 d is black, when theelectrophoretic particles 3 e are collected on the surface of the second electrode 5 as shown inFIG. 4 (a) by applying a positive-polarity voltage to the second electrode while keeping the voltage of thefirst electrode 3 c at 0 V, the cell looks white when viewed from above. On the other hand, when theelectrophoretic particles 3 e are collected on the surface of thefirst electrode 3 c as shown inFIG. 4 (b), by applying a negative-polarity voltage to the second electrode while keeping the voltage of thefirst electrode 3 c at 0 V, the cell looks black when viewed from above. By performing such a drive on a pixel-by-pixel basis, it is possible to display an arbitrary image or character by use of a multiplicity of pixels. - Hereinbelow, the present invention will be described more specifically based on Examples but the present invention is not limited thereto.
- A uniform mixture liquid was prepared by mixing 15 g of titanium oxide particles (average particle size: 0.2 μm) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 7 g of methacrylic acid and 130 g of methyl methacrylate. In a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein, the uniform mixture liquid was added. The resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension. Thereafter, the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere. After the polymerization, the resultant polymer particles were washed, followed by drying and classification to obtain white particles each comprising titanium oxide particle coated with (methacrylic acid-methyl methacrylate) copolymer. An average particle size of the particles was about 2 microns.
-
- Then, 5 wt. % of the
white electrophoretic particles 1 e, 2.5 wt. % of styrene-butadiene copolymer as a dispersion stabilizer, and 92.5 wt. % of anelectrophoretic dispersion medium 1 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) colored blue with 0.1 wt. % of a colorant (“Oil Blue N”, mfd. by Aldrich Co.) dissolved therein, were mixed to prepare an electrophoretic dispersion liquid. The electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown inFIG. 1 (a), which was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the imidazolium salt of the
electrophotographic particles 1 e was about 80 times that of an electrifying agent used in Comparative Example 1 appearing hereinafter, thus resulting in an excellent dissociation characteristic. As a result of the high degree of dissociation of the salt used, it was presumed that a resultant zeta potential was also increased to improve a charging performance. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of ±5 V, it was possible to effect clear blue/white display. Further, the
electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - A plurality of
microcapsules 1 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 1 were prepared by in-situ polymerization method. Each microcapsule was formed of urea-formaldehyde resin as a film-forming material. An electrophoretic display device shown inFIG. 1 (b) was prepared by disposing the plurality ofmicrocapsules 1 i on afirst substrate 1 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the imidazolium salt of the
electrophotographic particles 1 e was about 80 times that of an electrifying agent used in Comparative Example 1 appearing hereinafter, thus resulting in an excellent dissociation characteristic. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of ±5 V, it was possible to effect clear blue/white display. Further, the
electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - Particles of titanium oxide, coated with (methacrylic acid-methyl methacrylate) copolymer, prepared in the same manner as in Example 1 was subjected to two-stage polymerization with 2-ethylhexyl methacrylate to form a core-shell structure wherein a steric hindrance group was introduced into a surface of particle.
-
- Then, 5 wt. % of the
white electrophoretic particles 1 e and 95 wt. % of anelectrophoretic dispersion medium 1 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) colored blue with 0.1 wt. % of a colorant (“Oil Blue N”, mfd. by Aldrich Co.) dissolved therein, were mixed to prepare an electrophoretic dispersion liquid. The electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown inFIG. 1 (a), which was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the pyridinium salt of the
electrophotographic particles 1 e was about 40 times that of an electrifying agent used in Comparative Example 1 appearing hereinafter, thus resulting in an excellent dissociation characteristic. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of ±5 V, it was possible to effect clear blue/white display. Further, the
electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - A plurality of
microcapsules 1 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 3 were prepared by in-situ polymerization method. Each microcapsule was formed of urea-formaldehyde resin as a film-forming material. An electrophoretic display device shown inFIG. 1 (b) was prepared by disposing the plurality ofmicrocapsules 1 i on afirst substrate 1 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the pyridinium salt of the
electrophotographic particles 1 e was about 40 times that of an electrifying agent used in Comparative Example 1 appearing hereinafter, thus resulting in an excellent dissociation characteristic. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of ±5 V, it was possible to effect clear blue/white display. Further, the
electrophotographic particles 1 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 1, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - A uniform mixture liquid was prepared by mixing 10 g of carbon black particles (average particle size: 30 nm) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 7 g of sodium styrenesulfonate and 130 g of styrene. In a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein, the uniform mixture liquid was added. The resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension. Thereafter, the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere. After the polymerization, the resultant polymer particles were washed, followed by drying and classification to obtain black particles each comprising carbon black particle coated with (sodium styrene sulfonate-styrene) copolymer. An average particle size of the particles was about 2 microns.
- The particles were subjected to acid treatment to convert the sodium sulfonate into sulfonic acid group.
- With 10 g of the thus treated particles, 1 g of a quaternary ammonium salt represented by a structural formula (C) shown below was caused to react in methanol, followed by separation and purification to obtain
electrophotographic particles 3 e each having the quaternary ammonium salt. - Formula (C):
n-C16H33(CH3)3N+B− - In the present invention, however, the quaternary ammonium salt of the structural formula (7) may be caused to react with the particles without converting the sodium sulfonate into the sulfonic acid group to obtain electrophotographic particles 3 each having the quaternary ammonium salt.
- Then, 1 wt. % of the black
electrophoretic particles 3 e, 0.5 wt. % of styrene-butadiene copolymer as a dispersion stabilizer, and 98.5 wt. % of anelectrophoretic dispersion medium 3 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) were mixed to prepare an electrophoretic dispersion liquid. The electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown inFIG. 3 (a), which was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the imidazolium salt of the
electrophotographic particles 3 e was about 28 times that of an electrifying agent used in Comparative Example 2 appearing hereinafter, thus resulting in an excellent dissociation characteristic. As a result of the high degree of dissociation of the salt used, it was presumed that a resultant zeta potential was also increased to improve a charging performance. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of ±5 V, it was possible to effect clear black/white display. Further, the
electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - A plurality of
microcapsules 3 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 5 were prepared by in-situ polymerization method. Each microcapsule was formed of polyamide resin as a film-forming material. An electrophoretic display device shown inFIG. 3 (b) was prepared by disposing the plurality ofmicrocapsules 3 i on afirst substrate 3 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the quaternary ammonium salt of the
electrophotographic particles 3 e was about 28 times that of an electrifying agent used in Comparative Example 2 appearing hereinafter, thus resulting in an excellent dissociation characteristic. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of ±5 V, it was possible to effect clear black/white display. Further, the
electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - Particles of carbon black, coated with (sodium styrenesulfonate-styrene) copolymer, prepared in the same manner as in Example 5 was subjected to two-stage polymerization with dodecyl methacrylate to form a core-shell structure wherein a steric hindrance group was introduced into a surface of particle. The particles were then subjected to acid treatment to convert the sodium sulfonate salt into sulfonic acid group.
-
- Then, 1 wt. % of the black
electrophoretic particles 3 e and 99 wt. % of anelectrophoretic dispersion medium 3 f comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) mixed to prepare an electrophoretic dispersion liquid. The electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown inFIG. 3 (a), which was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the tertiary ammonium salt of the
electrophotographic particles 3 e was about 6 times that of an electrifying agent used in Comparative Example 2 appearing hereinafter, thus resulting in an excellent dissociation characteristic. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of +5 V, it was possible to effect clear black/white display. Further, the
electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - A plurality of
microcapsules 3 i each containing an electrophoretic dispersion liquid prepared in the same manner as in Example 7 were prepared by in-situ polymerization method. Each microcapsule was formed of polyamide resin as a film-forming material. An electrophoretic display device shown inFIG. 3 (b) was prepared by disposing the plurality ofmicrocapsules 3 i on afirst substrate 3 a by use of nozzles according to the ink jet method. The electrophoretic display device was connected with a voltage application circuit. - As a result of measurement of electric conductivity, it was confirmed that a degree of dissociation of the tertiary ammonium salt of the
electrophotographic particles 3 e was about 6 times that of an electrifying agent used in Comparative Example 2 appearing hereinafter, thus resulting in an excellent dissociation characteristic. - When the resultant electrophoretic display device was subjected to contrast display by driving it at a low voltage of +5 V, it was possible to effect clear black/white display. Further, the
electrophotographic particles 3 e had a response speed which was about several-ten times that of electrophotographic particles used in Comparative Example 2, so that it was confirmed that the electrophoretic display device was capable of being driven at high response speed. - A uniform mixture liquid was prepared by mixing 15 g of titanium oxide particles (average particle size: 0.2 μm) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 137 g of methyl methacrylate. In a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein, the uniform mixture liquid was added. The resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension. Thereafter, the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere. After the polymerization, the resultant polymer particles were washed, followed by drying and classification to obtain white particles each comprising titanium oxide particle coated with polymethyl methacrylate. An average particle size of the particles was about 2 microns.
- Then, 5 wt. % of the white electrophoretic particles, 0.5 wt. % of zirconium octate as an electrifying agent, 2.5 wt. % of styrene-butadiene copolymer as a dispersion stabilizer, and 92 wt. % of an electrophoretic dispersion medium comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) colored blue with 0.1 wt. % of a colorant (“Oil Blue N”, mfd. by Aldrich Co.) dissolved therein, were mixed to prepare an electrophoretic dispersion liquid. The electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in
FIG. 1 (a), which was connected with a voltage application circuit. - When the resultant electrophoretic display device was subjected to contrast display by driving it at the same voltage as in Examples 1 to 4, the electrophoretic display device failed to effect-clear blue/white display and achieve high-speed response.
- A uniform mixture liquid was prepared by mixing 10 g of carbon black particles (average particle size: 30 nm) which were subjected to hydrophobicity-imparting treatment and 1.7 g of azobisisobutyronitrile (AIBN) (polymerization initiator) in 135 g of styrene. In a dispersion medium comprising 1800 g of a sodium dodecyl sulfonate aqueous solution (concentration: 0.05 wt. %) and 90 g of calcium phosphate dispersed therein, the uniform mixture liquid was added. The resultant liquid was stirred at 10,000 rpm for 15 minutes by a homogenizer to prepare a suspension. Thereafter, the suspension was subjected to polymerization at 80° C. for 7 hours in a nitrogen atmosphere. After the polymerization, the resultant polymer particles were washed, followed by drying and classification to obtain black particles each comprising carbon black particle coated with polystyrene. An average particle size of the particles was about 2 microns.
- Then, 1 wt. % of the black particles, 0.1 wt. % of zirconium octate as an electrifying agent, 0.5 wt. % of styrene-butadiene copolymer as a dispersion stabilizer, and 98.4 wt. % of an electrophoretic dispersion medium comprising isoparaffin (trade name: “Isoper H”, mfd. by Exxon Corp.) were mixed to prepare an electrophoretic dispersion liquid. The electrophoretic dispersion liquid was injected into a cell by using nozzles according to an ink jet method to provide an electrophoretic display device, as shown in
FIG. 3 (a), which was connected with a voltage application circuit. - When the resultant electrophoretic display device was subjected to contrast display by driving it at the same voltage as in Examples 5 to 8, the electrophoretic display device failed to effect clear black/white display and achieve high-speed response.
- The electrophotographic particles according to the present invention can be utilized in the field of electrophotography or the like using an electrophoretic display device or liquid toner. The salt of the electrophotographic particles of the present invention has an excellent dissociation characteristic in an insulating solvent compared with an acid-base salt or an electrifying used, so that a charging performance is improved. As a result, it becomes possible to provide a considerably higher response speed of the electrophotographic particles than conventional electrophotographic particles. By using the electrophotographic particles capable of effecting high-speed response, it is possible to realize an excellent electrophoretic display device or electrophotographic apparatus.
- While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
- This application claims priority from Japanese Patent Application No. 117860/2004 filed Apr. 13, 2004, which is hereby incorporated by reference.
Claims (3)
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JP117860/2004(PAT.) | 2004-04-13 | ||
JP2004117860A JP2005300969A (en) | 2004-04-13 | 2004-04-13 | Electrophoresis particle, electrophoresis dispersion liquid, and electrophoresis display element using the same |
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US20050136347A1 (en) * | 2003-11-04 | 2005-06-23 | Haiyan Gu | Electrophoretic dispersions |
US20050267252A1 (en) * | 2004-05-31 | 2005-12-01 | Canon Kabushiki Kaisha | Electrophoretic particles and production process thereof |
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